Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple mobile devices. Base stations may communicate with mobile devices on downstream and upstream links. Each base station has a coverage range, which may be referred to as the coverage area of the cell. In some cases the coverage area may be subdivided into multiple cells. Also, in some cases, a base station may transmit multiple component carriers on different portions of available spectrum. These component carriers may also be referred to as cells.
A UE may be served by more than one carrier. In some cases a UE may be served by multiple carriers transmitted from a single base station, in other cases, a UE may be served by multiple carriers transmitted from more than one base station. When more than one carrier is configured to serve one or more UEs, there may be periods where one or more of the configured carriers may not transmit data to UEs. Continuing to transmit control information or reference signals when a carrier does not have data to transmit to the UEs may result in inefficient use of resources for the base station and for the UEs.